i 



Hollinger Corp. 
pH 8.5 




Concreting in 
Cold Weather 




Concreting in Cold Weather 

Advantages 

Concrete work is now carried on almost regardless of season and tem- 
perature. This is because the requirements leading to the success of con- 
crete work done when temperatures are low have become so generally 
known that contractors, cement products manufacturers, farmers and 
other users of concrete are now able to do concreting sometimes throughout 
the year, thus finding profitable employment for time that might otherwise 
be idle. 

By observing some simple and easily applied rules for preparing concrete 
mixtures, then using a few simple means to protect the freshly placed 
concrete, the resulting work will be just as successful as though carried on 
during warmer weather. The farmer can keep his farm hands busy dur- 
ing spare time in the winter, making concrete fence posts, concrete block, 
small concrete watering troughs and tanks, and laying barn and other 
interior concrete floors. 





Protecting newly laid concrete walk against possible freezing by applying a covering of hay or straw. 
This should be weighted down with pieces of short boards to prevent the covering from being blown away.^ 



Many concrete products plants take advantage of opportunities to keep 
their plants working throughout the year. A little expenditure of time is 
often all that would be necessary to fix one of the plant buildings so that 
it could be made a comfortable workroom for carrying on the manufacture 
of the plant's specialty or specialties throughout the winter. 




I ft &*/ 

CONCRETING IN COLD WEATHER 3 

Concrete work done when the average temperature is below a certain 
point may cost a little more than the same kind of work done under the 
usual summer conditions. On the general run of contracting this cost 
seldom runs more than 10 per cent above that of work done in warm 
weather and frequently not more than 6 per cent — sometimes even less. 
Part of this extra expense comes from applying necessary protective meas- 
ures, and part results from the lower efficiency of workmen through expo- 
sure to the cold. Some of the increased cost may be due to the added time 
necessary for the concrete to harden, which prevents such speedy progress 
of the work as would be possible in warm weather. 

Contractors have found that prospective builders are usually willing to 
pay any slight extra cost of work done in cold weather for the certainty of 
having their buildings completed and ready for use at an earlier date. 

Effect of Low Temperatures on Concrete Work 

Heat hastens the hardening of concrete; cold delays it. The effect of 
cold becomes noticeable in this respect when temperatures fall below 50 
degrees Fahrenheit, and becomes more marked as temperatures continue 
to fall. 

The general opinion is that freezing will not injure concrete that has 
first had an opportunity to harden for at least 48 hours under favorable 
conditions. If, before early hardening has taken place, concrete is allowed 
to freeze and thaw at short intervals, it will be damaged to some extent. 
As a rule, concrete will not show any serious effects from having once been 
frozen if, after it thaws out, it is not again frozen until early hardening is 
complete. -But it is far better to protect the concrete from freezing for 
from 48 hours to four or five days, depending upon the degree of the cold, 
rather than to expose it to the possibility of freezing. If such protection 
is given, no injury need be feared when the concrete is finally exposed to 
freezing temperatures. 

Some of the requirements leading to success with concrete work done 
in cold weather are self-evident when one remembers the conditions under 
which concrete hardens and gains strength in warm weather. Warmth 
and moisture are necessary to the proper hardening of concrete. Any 
means that will cause these two conditions to be present in cold weather, 
particularly during the period of early hardening, will lead to the success 
of concrete work done at such times, if all other good practice is also 
followed. 

Heating Materials 

If sand and pebbles or broken stone and mixing water are heated, the 
concrete mixture will be so warmed that more rapid early hardening will 
take place. Warmth given the concrete from heated materials can 
readily be held in it for some time — as long as may be necessary to com- 
plete early hardening — if the concrete is placed quickly after mixing and 
at once protected in some one or more of the several ways that will be 
described later. 

Additional heat is also developed in „he concrete mass as a result of 



4 CONCRETING IN COLD WEATHER 

changes taking place from the chemical combination of the cement and 
water. This also helps to keep up the temperature of the freshly placed 
concrete and thus aids to protect it from freezing. As cement forms only 
a relatively small bulk of a concrete mixture, it need not be heated, but it 
should be stored where it will be protected from dampness and extreme 
cold. 




Aggregates being heated by thrusting steam pipes into the material as received loaded on cars. 



Heating Water 

Mixing water is the easiest of the materials to heat. It can readily be 
heated to 150 degrees Fahrenheit, and kept at this temperature until 
used, by one of several methods. Two methods are in common use for 
heating mixing water; one is to use live or exhaust steam from a steam 
boiler, and the other is to heat the water in tanks or kettles over a fire. 
On large contracting jobs mixing water is usually heated by steam. If a 
steam engine is used to run the mixer, the exhaust steam is often allowed 
to discharge into a water tank that is a fixture on the mixer. This arrange- 
ment is satisfactory, but does not heat as rapidly as live steam. 

Lave steam, which is steam under pressure, furnishes more heat where 
considerable quantities of water are required at regular intervals. When 
live steam is used and the water has been heated as required, its tempera- 
ture can readily be kept at the desired point by a regulating valve that will 
admit only enough steam to the water to keep it hot. An old steam boiler 
that is no longer safe for carrying high steam pressures may sometimes be 
used as a source of steam supply, since a boiler pressure of 25 pounds is 
sufficient for the purpose. 



CONCRETING IN COLD WEATHER 5 

On small jobs a tank or large kettle supported above a fire may supply 
all the heated water that is needed. Coils of pipe similar to steam radia- 
tor coils have been supported above a fire and water allowed to flow slowly 
through the coils and into a barrel, the water being heated as it passed 
through the coils. In such a case also after the required amount of water 
has been heated, it can be kept at the desired temperature by allowing no 
more water to pass through the coil than can be converted into steam, 
this being discharged into the barrel. 

Heating Sand and Pebbles or Broken Stone 

Unless sand and pebbles and broken stone are stored indoors during the 
winter, they are certain to contain frost, and sometimes lumps of snow and 
ice. Frozen materials should not be used in concrete mixtures. They 
not only chill the concrete, but prevent thorough mixing. Sand and peb- 





Materials may be heated by thrusting steam pipes into them and covering the piles with canvas to 
retain the heat thus given. 



bles or broken stone should be heated. A temperature not exceeding 
150 degrees Fahrenheit will generally prove sufficient. Too much heat 
will injure some kinds of sand and pebbles or broken stone, particularly 
limestone. 

On small jobs these materials are usually warmed by piling them over 
and around sheet iron cylinders, such as an old smokestack, a section of 
old iron sewer or culvert pipe, or an old steam boiler. A fire is built within 
and the materials to be heated piled around and upon this "stove." Some- 
times a stove is built by using concrete block for a foundation and covering 
with a piece of sheet steel such as boiler plate. It is necessary to turn or 



6 CONCRETING IN COLD WEATHER 

rake over the materials frequently so that those nearest the fire will not 
become too hot and thus possibly injured, while at the outside and edges 
of the pile they may not be warmed. 

Separate stoves are best for heating sand and pebbles, although some- 
times a pipe stove may be long enough so that sand can be piled at one 
end and pebbles or broken stone at the other. Care should be used to 
keep the two materials separate, otherwise when taking them from the 
pile to proportion a batch of concrete, some batch is likely to be improperly 
proportioned because of the sand and pebbles having become mixed 
before measuring. 

Heating sand and pebbles or broken stone by steam has advantages 
over other ways. They may be piled directly on steam-heated pipe coils 
or the piles may be covered with tarpaulins and steam applied directly 
to the materials. The tarpaulins act to house in the piles and thus to 
hold the heat. With a steady supply of steam this method of heating is 




Many buildings such as this have been built by experienced contractors during freezing weather by 
housing in various floors of the structure as the work has progressed. 



quite effective. The pipes used are closed at one end and perforated 
along their lower side by numbers of very small holes. The other end of 
the pipe is connected to the source of steam supply by means of steam 
hose. The pipes are then stuck into the piles of materials and steam 
turned on. 

While cold weather concreting is in progress, piles of sand and pebbles 
or broken stone exposed to the weather should be kept covered with tar- 
paulins to prevent the materials from becoming water-soaked and possibly 
frozen solid if the temperature should drop suddenly. 



CONCRETING IN COLD WEATHER 



Use of Salt in Mixing Water 

Water containing common salt, calcium chloride (chloride of lime) and 
a number of other chemicals will not freeze at the same temperature as 
water which contains none of these substances. For this reason, it was 
common when concrete work was first done in cold weather, to add salt 
to the mixing water to prevent the concrete from freezing. As not more 
than 10 per cent of salt can safely be used without danger of affecting the 
final strength of the concrete and as such a quantity of salt gives protec- 
tion only against a possible drop of temperature of 10 degrees below freez- 
ing, the use of salt is not effective when cold is extreme. Resides, salt 
does not accomplish the one thing most desirable. It delays instead of 
hastens the hardening of the concrete. Salt is considered objectionable 
in reinforced concrete because it may corrode the reinforcing steel. Salt 
should not be used where the appearance of the finished work would be 
spoiled by the whitish deposit that may later appear on the surface. This 




Protecting freshly laid concrete building floors. One salamander used for each 300 square feet of 
floor surface. Tarpaulins hung over the sides of the building assist to retain the heat made by these stoves 
and to exclude the cold. 

deposit is commonly referred to as efflorescence and may be expected on 
work in which salt has been used. 

In general, calcium chloride (chloride of lime) is also objectionable for 
reasons similar to those mentioned for salt, although experiments con- 
ducted by the United States Rureau of Standards indicate that there 
may be a possible advantage in using it in some cases, because a 4 per cent 
solution in water seems to hasten the hardening of concrete. The use of 
calcium chloride is said to increase the cost of concrete work from 12 to 
15 cents per cubic yard. 



8 



CONCRETING IN COLD WEATHER 



Heating Forms 

Before placing concrete in cold weather forms should be thoroughly 
cleaned of snow, ice or particles of frozen concrete. Metal forms should 
always be heated. In extremely cold weather wood forms also should be 
heated. Turning a jet of steam against form faces is best when available. 

Protection to be Given 

In the following paragraphs a number of ways of protecting concrete 
work done in cold weather will be described. Usually no one of these 
methods or ways is used alone. Generally two or more of them are com- 
bined. 




Concrete grain bins built during freezing weather by using canvas covering to retain heat given by 
salamanders kept burning inside the bins. On this particular job concrete was mixed by hand in the struc- 
ture beneath this protection. 

After forms have been cleaned of ice, snow and any particles of frozen 
concrete, and have been warmed, the concrete mixture should be placed 
immediately so that none of the warmth given to it by the heated materials 
will be lost. All of the work should be done as quickly as possible. 

Thin floor slabs, beams, columns, sidewalks, feeding floors, barnyard 
pavements and similar classes of work have a large surface area compared 
with their volume; therefore, more careful protection must be given to 
such work than to foundations, abutments and other mass construction 
where the excavation or the bulk of the mass and heavy forms give part 
of the required protection. Floors are usually protected by a covering 
of hay or straw. Building paper or canvas should first be laid over the 
concrete, then from 6 to 12 inches of straw, depending upon the tempera- 
ture to be protected against. If the work is out of doors the covering 



CONCRETING IN COLD WEATHER 9 

should be weighted down with short boards to prevent it from being 
blown away. Sidewalks, feeding floors and similar outdoor pavements 
must receive extra care. Sometimes walks in business districts are housed 
in by means of a canvas-covered frame and the enclosure kept warm by 
steam or open coke-burning stove pots, commonly spoken of a3 salaman- 
ders. 

When forms are tight and made of heavy material, mass work may 
require no other protection than covering the concrete exposed at the top. 
This protection can be given by a layer of hay or straw, while vertical 
faces may be given additional protection besides that given by the forms 
by building a rough lattice work of strips 10 or 12 inches from the outside 




Concrete sidewalks in business sections have often been made during cold weather by housing in as 
here shown and keeping the enclosure at proper temperature by using salamanders. 



face of forms and fining in between lattice and forms with straw or manure. 
Such extreme measures are usually required only when the cold is very 
severe. 

If manure is used as a covering, it should never be placed directly upon 
the fresh concrete. It is not only likely to stain the work, but may injure 
the surface by causing a slight pitting or scaling. This is probably due 
to the fact that sometimes nitric acid is formed when the manure rots and 
this chemical is probably the substance that has caused injury to concrete 
surfaces protected by manure covering, in those cases observed in the past. 

Foundations can easily be protected because the greater portion of the 
work is in an excavation. Forms, or earth walls of the trench gives enough 
protection to the sides of the work if the cold is only moderate. There 
remains nothing but the top surface to be covered. 



10 



CONCRETING IN COLD WEATHER 



Barn and stable floors built during winter should be laid in such sections 
that a portion of the old floors may be used while concreting is in progress. 
This is necessary because of the longer time that concrete requires for 
hardening in cold weather to be safe for use. 

For such indoor work little additional protection is needed besides that 
given by the enclosing structure. Temperature may be kept as desired 
by oil stoves. Care should be taken, however, to prevent the possibility 
of fire. This also applies where salamanders or open coke-burning stoves 
are used to supply heat. It is a wise precaution always to have an attend- 
ant on the job as a measure of safety against the spread of fire. 




Newly laid floor housed in by building a scantling frame and covering with canvas. The enclosure 
is heated by salamanders kept burning beneath this covering. 



Removing Forms 

Although too early removal of forms is to be avoided regardless of season, 
this statement applies with great force to work done during cold weather. 
Especially is this true of concrete walls, roofs, and overhead floors which are 
intended to carry loads other than their own weight. Forms should be 
left in place until it is absolutely certain that the concrete has become 
strong enough to be safe. Frozen concrete often has the appearance of 
thoroughly hardened concrete. If struck with a hammer it will ring just 
like hardened concrete. The work should be examined carefully before 
forms are removed. A single section of the forms or part of a section may 
be removed to expose the concrete, then the flame from a plumber's blow 
torch, a jet of steam or hot water may be directed against the concrete 
surface. If merely frozen the heat will thaw the water in the concrete, 
thus showing the condition of the work. 



CONCRETING IN COLD WEATHER 



11 



Gold Weather Concrete Work on the Farm 

There is much concrete work on the farm that may be carried on during 
cold weather. Farm hands may thus be kept at work when they might 
otherwise be idle. Concrete block, fence posts, small watering and feeding 
troughs can be made indoors. 

A convenient room for carrying on cold weather concrete work indoors 
can usually be arranged by fixing up some portion of a shed, barn or cellar. 
Sand and pebbles should be brought into the workroom and stored until 
desired for use. The workroom temperature should be kept at not lower 
than 50 degrees Fahrenheit. If the materials are stored in such a tem- 
perature, frost or frozen lumps of material that may have been in them will 




Reinforced concrete fish packing building at Portland, Me., during the winter weather. Concrete 
work was made possible by observing all precautions described in this booklet and by housing in the work 
as shown with canvas. 

disappear if the piles are well raked over occasionally. Materials containing 
frost or frozen lumps must not be used in concrete mixtures. If the work- 
room is not large enough to store a considerable quantity of materials and 
they must therefore be brought indoors as required for use, some means 
for heating them must be arranged. 

Care must be taken to prevent concrete block, fence posts and similar 
products from freezing during the first two or three days after made. They 
should be stored for a long time before being used, preferably until spring. 

Cold Weather Concrete Work for Concrete Products Plants 

In general, the recommendations already given for doing concrete work 
in cold weather apply to the manufacture of concrete products at com- 
mercial plants. Many such plants have buildings that do not permit 






12 



CONCRETING IN COLD WEATHER 



the operation of the plant 
twelve months a year. In 
most cases they could be fixed 
up at little expense and the 
plant be profitably operated 
all the year. 

Workrooms and hardening 
rooms or chambers should be 
so arranged that drafts of 
cold air will be prevented 
from striking the freshly-made 
concrete products. The work- 
room temperature should be 
kept at not lower than 50 
degrees Fahrenheit. 

Modern plants harden their 
concrete products by steam. 
This is a great advantage at 
any time of year, but particu- 
larly so in cold weather. 

In all cold weather concrete 
work the size of concrete 
batches mixed should be so 
regulated that each batch may 
be quickly used in the molds 
or forms. The mixed concrete 
should not be exposed before 

placing so that it may lose some of the warmth given it by heated 

materials. 

Of Interest to the Contractor 

Concrete contractors who are prepared by experience and equipment to 
keep their forces employed during cold weather know the profits resulting 
from thus lengthening their working season. Their equipment is usually 
such that it is easy for them to apply the precautions that have been 
described in this booklet as necessary. One large construction company 
in the East makes cold weather concreting almost a specialty. This, 
however, should not cause contractors in general to look at this class of 
work as one in which they also should specialize. Long experience with 
cold weather concreting is necessary for success on large jobs. 

The last edition of the Ruilding Code Recommended by the National 
Roard of Fire Underwriters, New York, devotes some space to measures 
that are recommended in connection with cold weather concreting. Among 
other things, this code suggests that "when concrete has been deposited 
while the outside temperature was above 40 degrees Fahrenheit with a 
rising temperature," that ample supports be left to carry the construction 
until it is undoubtedly safe to remove them. This code further recom- 
mends that "a special permit should be obtained for removal of forms from 
concrete deposited when the outside temperature was below 32 degrees 




Concrete pipe protected by canvas covering and setting a 
lighted lantern in each pipe. 



CONCRETING IN COLD WEATHER 



13 



Fahrenheit and the number of days required should be increased in pro- 
portion to the amount of time the temperature remained below 32 degrees 
Fahrenheit after the concrete was deposited." 

For the contractor not thoroughly experienced in cold weather concrete 
work it is recommended that, when the average temperature for the day 
is between a minimum of 40 and a maximum of 50 degrees Fahrenheit, the 
building in or on which work is being carried on should be enclosed. When 
the average temperature is below 40 degrees and above 35 degrees Fahren- 
heit, the materials should be heated. When the average temperature 
falls below 35 degrees Fahrenheit, the building should be heated by sala- 
manders or similar means so that the interior temperature surrounding the 
concrete work will always be higher than 40 degrees. 

Occasionally it is necessary for the contractor to make some provision on 
the job for the comfort of his workmen. Shelters or wind shields have 
been built around benches where carpenters are building forms, as well as 
around the concrete mixer to protect the men. Where excavating is 
going on in the open, it is best to have a small shanty with a good fire where 




Concrete construction at Pabos, Quebec, carried on during severe winter weather. This work was 
housed in as it progressed, and usual precautions used to prevent freezing. 

the men can warm themselves occasionally. Other means of furnishing 
reasonable comfort for men working under unfavorable temperature 
conditions will suggest themselves to the experienced contractor. 

Facts to Remember 

REMEMBER that during the first few days following the placing of 
concrete, alternate freezing and thawing at comparatively short intervals 
will damage it. 



14 CONCRETING IN COLD WEATHER 

REMEMBER that although concrete which freezes before early 
hardening has been completed may not be permanently injured, if after 
thawing out it is not again exposed to freezing until hardened, protecting 
the concrete against possibility of freezing is best. 

REMEMBER, therefore, that it is necessary to so mix, place and 
protect the concrete that early hardening will be complete before the work 
is exposed to freezing temperatures. 

REMEMBER that to do this: 

(1) Sand and pebbles or broken stone used must be free from frost or 
lumps of frozen materials. 

(2) If these materials contain frost or frozen lumps, thaw them out 
before using. 

(3) As cement forms but a relatively small bulk of the materials in any 
batch of concrete, it need not be heated. 

(4) Mixing water should always be heated. 





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Finishing granolithic floors in freezing weather. The work has been housed in and salamanders are 
burning to keep the temperature where desired. 

REMEMBER that although adding common salt to mixing water will 
prevent freezing of concrete that has not hardened, there is a limit to the 
quantity of salt which may be added if the final strength of the concrete is 
not to be affected. Salt simply lowers the freezing point of the mixing 
water; it does not supply what is most needed — heat and warmth. It 
delays, instead of hastens, the hardening of the concrete. 

REMEMBER that sand and pebbles or broken stone and mixing water 
must be heated so that the concrete when placed shall have a 
temperature of from 75 to 80 degrees. 

REMEMBER that some sands are injured by too much heat. The 
same applies to certain varieties of pebbles and broken stone. A temper- 



CONCRETING IN COLD WEATHER 15 

ature not exceeding 150 degrees Fahrenheit will generally prove most 
satisfactory. 

REMEMBER to place concrete immediately after mixing so that 
none of the heat will be lost before placing in the forms. 

REMEMBER to warm metal forms and reinforcing before placing 
concrete. Be careful to remove ice and snow and frozen concrete remain- 
ing on the forms from preceding work. Forms can be warmed by turning 
a jet of steam against them or by wetting with hot water. 

REMEMBER that even though materials have been heated and the 
concrete placed immediately after mixing, it will lose much of its heat if 
not protected from low temperatures. 

REMEMBER, therefore, to protect the concrete immediately after 
placing. Canvas covering, sheathing, housing-in the work, or hay or straw, 
properly applied will furnish the required protection for some work. In 
addition to these means, small oil or coke-burning stove or salamanders 
may be used in enclosed structures. 

REMEMBER that temperatures which may not be low enough to 
freeze the concrete may, nevertheless, delay its hardening for a con- 
siderable time. Do not expect concrete placed when the temperature is 
low and remains low for some time afterward to be safe for use as soon 
as though placed during warmer weather. 

REMEMBER that if concreting is unavoidably delayed or interrupted 
the work should be covered until concreting is again begun. 

REMEMBER to cover and protect any section of the work as soon as 
completed. In severe cold weather, continue this protection for at least 
five days. 

REMEMBER that forms must not be removed from the concrete 
work too early. This applies to any concrete work, regardless of season, 
but is particularly important with work done during cold weather. 

REMEMBER that frozen concrete sometimes very closely resembles 
concrete that has thoroughly hardened. When frozen concrete is struck 
with a hammer, it will often ring like properly hardened concrete. Before 
removing forms, examine the work carefully to see whether it has hardened 
or is simply frozen. To determine this, remove one board from some 
section of a form, pour hot water on the concrete or turn the flame of a 
plumber's blow torch or a jet of steam under pressure against the concrete. 
If frozen, the heat will soften the concrete by thawing the water contained 
in it. 

REMEMBER— SAFETY FIRST. 



liiSwiSr 0F C0NGRESS 

020 187 551 ] 



Concrete Fence Posts 

Concrete Feeding Floors, Barn- 
yard Pavements and Concrete 
Walks 

Proportioning Concrete Mixtures 
and Mixing and Placing Con- 
crete 

Concrete Foundations 

Concrete Troughs, Tanks, Hog 
Wallows, Manure Pits and 
Cisterns 



Jlre names of some of our booklets that 
will give you helpful ideas for filling in 
spare hours with concrete Work m C °W 
weather. If interested in ami of these 
subjects, mite the Portland Cement 
Association, 111 West Washington 
Street, Chicago. 



"Concrete for Permanence" 



Hollinger Corp. 
P H 8.5 



B 



LIBRARY OF CONGRESS 



020 187 551 1 



Hollinger Corp. 
pH 8.5 



